Backlighting is generally necessary in all Liquid Crystal Displays (LCDs). Such displays may be used in televisions, lap-top computers, and various types of aircraft and automotive displays. The backlight in these systems is normally provided from a miniature fluorescent lamp. In many of these applications the backlight is the largest single consumer of power in the display system. There is clearly a need for high efficiency, versatile lamps for applications with LCDs.
The efficiency of electric lamps using filaments has not increased significantly for many years. Fluorescent discharge lamps are more efficient, but have other limitations which have been difficult to remove, such as the potential for environmental pollution from mercury in the lamps.
Cathodoluminescent lamps have been known for several years. They originally employed thermionic cathodes. U.S. Pat. No. 4,818,914 provided an improvement in cathodoluminescent lamps based on a field emission cathode. A layer of phosphor on an anode is located inside an envelope along with the field emission cathode, which is placed opposite the phosphor layer. A voltage source, either DC or AC, is connected across the cathode and accelerator electrodes to cause field emission of electrons from tips of needle-like members. A higher voltage is connected across the cathode and an anode for attracting electrons to the phosphor layer and exciting the phosphor to luminescence.
In aviation and automobile displays, particularly, there is a need for a light source that can be dimmed and that does not fail catastrophically. For other types of displays and light sources, such as projectors, a high brightness is needed. In some applications it is important to have the capability to scale-up the size of the source to provide high total light output. In all light sources, there is a need for a simple and efficient source and a source that will not cause environmental pollution.